1. Field of the Invention
The present invention relates generally to a structure for a phase change memory cell and a method of manufacturing the phase change memory cell. More particularly, the present invention relates to a phase change memory cell structure, having a switching current path that is confined to a region smaller than the potentially switchable volume of the phase change material.
2. Description of the Related Art
Resistance switching materials (i.e., phase change materials), including but not limited to chalcogenides and alloys thereof, and perovskites or perovskite-like materials (e.g., colossal magnetoresistance (CMR) materials and high temperature superconductivity (HTSC) materials), can switch between an amorphous state, semi-amorphous or semi-crystalline states, and a crystalline state, depending upon the voltage of current passed through them. In their amorphous states, these phase change materials exhibit a higher resistance. In their crystalline states, resistance switching materials exhibit a lower resistance because electrons are able to move fast through the material. Electrical impulses applied to theses materials can “tune” or “program” them, such that they exhibit the desired resistive property. The following U.S. Patents and U.S. Patent Applications (incorporated herein by reference) discuss phase-change materials and methods for switching the resistances of such materials: U.S. Pat. No. 6,673,691 issued to Zhuang et al. on Jan. 6, 2004; U.S. Pat. No. 6,204,139 issued to Liu et al. on Mar. 20, 2001; and, U.S. Patent Application Pub. No. US 2004/0252544, Lowery et al., Dec. 16, 2004. Recently, the availability of binary chalcogenide alloys such as doped SbTe and ternary chalcogenide alloys such as those composed of Germanium, Antimony and Tellurium (e.g., Ge2Sb2Te5 (GST)), as well as progress in lithographic and deposition techniques have provided new momentum towards the realization of practical phase change memory (PCM) cells for memory or storage applications, for example, as illustrated in the following documents (incorporated herein by reference): U.S. patent application Ser. No. 10/766,936, Sun et al., filed Jan. 30, 2004; “Electronic Switching in Phase-Change Memories”, Pirovano et. al, IEEE Transactions on Electron Devices, Vol. 5, No. 3, pgs. 452-459, March 2004, “Amorphous non-volatile memory: the past and the future”, Neale, Electronic Engineering, April 2001; “A GeSbTe Phase-Change Memory Cell Featuring a Tungsten Heater Electrode for Low Power, Highly Stable, and Short-Read-Cycle Operations”, Takaura et al., 0-7803-7873-3/03© 2003 IEEE; U.S. Patent Application Pub. No. US 2004/0036065 A1, Doan et al., Feb. 26, 2004; and U.S. Patent Application Pub. No. US 2003/0219924 A1, Bez et al., Nov. 27, 2003. However, creating a phase change memory cell with power demands that are compatible with the current state-of-the-art integrated circuit design rules can be difficult.